The present invention generally relates to fabrication of semiconductor devices and more particularly to a mold used for molding a resin semiconductor package body. More specifically, the present invention relates to a mold for molding a resin package body of a semiconductor device by a press-molding process.
With ever-continuing trend of miniaturization of electronic apparatuses and devices, intensive efforts are being made on miniaturization of semiconductor devices and integrated circuits. As an ultimate package form of such miniaturized semiconductor devices and integrated circuits, there is a concept of so-called chip-size package in which the size of the semiconductor package is reduced to the size of a semiconductor chip.
In another aspect, such a miniaturization of semiconductor integrated circuits has brought the tendency of ever-increasing integration density, while such an increase of the integration density has raised the problem of excessively narrowed pitch for interconnection pins used in semiconductor integrated circuits for external connection. In order to overcome the foregoing problem of narrow pitch of interconnection pins, there is a proposal of so-called ball grid array, in which bump electrodes are arranged two-dimensionally on a major surface, such as a bottom surface, of a semiconductor chip. By using a ball grid array, it is possible to increase the number of interconnection pins substantially, while simultaneously reducing the overall size of the semiconductor device.
As such a bump electrode, provided on a pad electrode of a semiconductor chip, is mechanically fragile, there is a proposal to cover the bottom surface of the semiconductor chip, on which the bump electrodes are provided, by a thin layer of potting resin. By providing such a thin layer of potting resin, not only the bump electrodes are protected but also the bottom surface of the semiconductor chip, on which a number of semiconductor devices are formed. In order to use the foregoing promising construction, it is necessary to establish the technology to cover the bottom surface of the semiconductor chip by a thin layer of potting resin.
A resin film can be formed on a semiconductor chip by various processes including a transfer molding process, an injection-molding process, a press-molding process, and the like, wherein the press-molding process is a promising process for forming such a thin resin film on a semiconductor device in view of the low cost of the process and the inexpensive facility for conducting the process.
In a press-molding process, a mold formed of a lower mold and an upper mold are used, wherein the lower and upper molds are held on a press in a state that a semiconductor device or wafer is held between the lower mold and the upper mold together with a resin tablet of a thermosetting resin. In operation, the press is activated in the state that the lower and upper molds are heated, wherein the resin tablet undergoes a melting and a thin resin film is formed so as to cover the semiconductor device. By curing the resin film thus formed, it is possible to form the desired resin protective film covering the surface of the semiconductor device.
These days, the bump electrodes formed on a semiconductor device generally have a reduced size of 25-50 xcexcm as a result of device miniaturization. In the case of such highly miniaturized semiconductor devices, it is necessary to form the resin film on the surface of the semiconductor chip, on which the bump electrodes are formed, such that the resin film has a thickness of about 100 xcexcm or less. Formation of such a thin resin film by a press molding process requires an exact parallelism between the upper mold and the lower mold at the time of the molding process.
With development in the art of mold manufacturing, the upper mold and the lower mold can be manufactured with exact size and shape. On the other hand, conventional press molding process has used the lower mold and the upper mold in the state that they are rigidly fixed on an upper platen and a lower platen each forming a press head. In such a construction, it will be noted that the lower mold and the upper mold no longer have a degree of freedom to move with respect to the lower and upper platens. Thereby, the parallelism between the lower mold and the upper mold is easily lost when there is a minute deviation from exact parallelism in the geometrical relationship between the upper and lower platens, and it has been difficult to form the desired thin resin film on the surface of the semiconductor chip by a press-molding process.
Accordingly, it is a general object of the present invention to provide a novel and useful mold used for fabricating semiconductor devices and a fabricating process of a semiconductor device using a press-molding process wherein the foregoing problems are eliminated.
Another and more specific object of the present invention is to provide a mold used for fabricating semiconductor devices wherein an exact parallelism is maintained between an upper mold and a lower mold irrespective of the precision of a press head used for pressing the mold.
Another object of the present invention is to provide a mold, comprising:
an upper mold; and
a lower mold disposed so as to face said upper mold,
said upper mold comprising:
a press plate; and
a fixing mechanism adapted to be mounted on a press head,
said fixing mechanism carrying said press plate movably such that said press plate is tiltable with respect to a nominal plane perpendicular to a direction connecting said upper mold and said lower mold.
Another object of the present invention is to provide a mold, comprising:
an upper mold; and
a lower mold disposed so as to face said upper mold,
said lower mold comprising:
a base block adapted to be mounted on a press head;
a center block provided on said base block;
an inner die provided on said center block so as to face said upper mold;
a guide ring provided so as to surround said center block laterally, said guide ring being movable relatively to said center block in a direction of a force exerted by said press when conducting a press-molding process;
an outer die provided on said guide ring so as to face said press plate; and
a rolling body disposed in a gap between an outer periphery of said center block and an inner periphery of said guide ring.
Another object of the present invention is to provide a method of fabricating a semiconductor device by a press-molding process of a resin package body, comprising the steps of:
mounting a semiconductor wafer and a resin tablet on an inner die of a lower mold, said inner die being surrounded by an outer die forming a part of said lower mold together with said inner die, said outer die being movable with respect to said inner die in a direction perpendicular to a plane of said inner die;
lowering a press plate forming an upper mold in a state that said press plate is held in a tiltable manner with respect to a press head, by activating said press head, such that said press plate engages said outer die in a state that said outer die forms, together with said inner die, a space for accommodating said semiconductor chip and said resin tablet;
locking said press plate with respect to said press head in a state in which said press plate is engaged with said outer die;
causing said resin tablet to melt;
lowering a press plate further and simultaneously lowering said outer die with respect to said inner die, such that a volume of said space is reduced.
According to the present invention, the upper mold and the lower mold are held in exact parallelism even when there is a deviation from parallelism in the press head used for pressing the upper and lower molds with each other. Thereby, a thin resin film is formed on the surface of a semiconductor chip with a uniform thickness.